The current methods for removing hair from the human body, by shaving, as opposed to epilation, involve two basic approaches: the razor approach, wherein a very sharp blade is pushed against the skin at an angle, thereby cutting hair; and the screen approach, wherein a thin fenestrated metal screen is moved across the skin, exposing hair though the holes and cutting them by a mechanized, typically motorized, cutting element.
In the sharp razor blade approach, the energy for cutting is provided by the hand driving the razor across the skin of the user, typically by the hand of the user him/herself, and the hair is cut by the impact force applied thereon and by virtue of its stiffness. The conditions of cutting hair are a compromise between the ease of cutting a soft (or softened) hair (or hair bristle) and having the necessary counter-force against the blade's impact which can only come from the hardness of the hair bristle. Apart from being a compromise difficult to optimize daily on a variety of hair bristles, the sharpness of the blade and its angle pose a constant risk of nicks and cuts, as the blade is driven forcefully across the skin.
In the screen approach of most motorized shaving apparatus, the problem of safety is mitigated since the skin and the cutting elements are separated by the screen. Moreover, the hair bristles which penetrate the screen through its holes are given a prop to be cut against; hence, the lack of a counter-force for cutting is also mitigated to some extent. However, in order to arrive at an efficient cutting condition, the hair bristle must enter a hole and be perpendicular to the skin, requirements which are not always met unless the screen is constantly moved across the skin. Still, when the hair bristle is eventually cut at the optimal angle, it cannot be cut close to the skin due to the separating screen.
One cutting technique which requires minimal force for cutting hair can be effected by scissors. Scissors cut hair at the crossing point of two blades which do not have to be very sharp in order to cut the hair due to the fact that the blades contact the hair from substantially opposite directions in the plane of cutting, mutually providing each other with a counter-force for cutting. While it is impractical to use scissors for daily shaving, which requires maximal closeness of the cutting point to the skin, the scissors cutting technique was implemented in the form of rotary cutter units cutting hair against a flat and straight stationary blade. This hair cutting technique is capable of providing a very close shave since the cutting blades are positioned flush against the skin at the time of cutting. This also renders this cutting approach relatively safe from accidental cuts.
However, the presently known configurations which have attempted to implement this technique have suffered, among other drawbacks, from improperly positioned driving mechanisms, which were placed outside of the shaving head, moving the rotary cutter unit by means of a direct shaft, or indirectly by means of external gears, bevel gears, worm gears, sprockets, belt and pulley mechanisms and the like. Essentially, these external driving mechanisms suffer from loss of kinetic energy, leading to limited rotation speed of the rotary cutter unit, and therefore provide poor shaving results. Moreover, all these external driving mechanisms lead to cumbersome designs, large size and substantial weight of the resulting shaving device since they house the drive mechanism alongside or perpendicularly to the shaving head. In addition, they require large powerful motors with or without portable power sources.
For example, one rotary razor exists that comprises a casing provided with a slot, a cutting edge formed along one edge of the slot, guards projecting from the opposite side of the slot to a point immediately adjacent the cutting edge, the cutting edge and the guards being rigid with respect to the casing, and a rotary cutter within the casing arranged to co-act with such cutting edge. The rotary cutter in this rotary razor is provided with an adjustment means whereby it may be set at a point in close proximity to the first named cutting edge but not in frictional contact therewith, such means comprising bearings within the casing. The bearings each have a pair of projecting arms and the casing is provided with a slot adjacent each arm. Set screws project through the slots and into the arms while another arm projects from each pair of arms at right angles thereto. The set screws project through the casing and into the last named arms. This rotary razor provides a rotary cutter shaving device wherein the rotary cutter unit is pressed and held against the stationary blade in order to effect a close and effective shave. However, in this rotary razor, the drive mechanism is not part of the shaving head or hair-cutting head.
A shearing tool also exists with a tapered cylindrical cutter held by bearings inside a housing. The housing is formed with a slot, wherein one of the edges of the slot constitutes a cutting edge cooperating with the cutting edges of the tapered cylindrical cutter. In this shearing tool, a shaft extends out of the hair-cutting head and the drive mechanism is not part of the hair-cutting head.
Another rotary razor exists having a casing formed with a longitudinal slot, a rotary shaft, a series of filler blocks encircling the shaft, a series of razor blades engaged between the filler blocks and having their edges projecting spirally beyond the outer face of the filler blocks. Upon rotation of the shaft, the razor blades pass across the slot opening of the casing. A plate on the casing is arranged along one edge of the slot in a position to contact the cutting edge of the spirally positioned blades on the shaft. While this rotary razor provides a solution to the production of the rotary cutter unit, the drive mechanism is outside the hair-cutting head.
Another shaver exists comprising a tubular casing formed with a longitudinally extending slot and with comb teeth or fingers extending transversely to the slot. A rotor is locate within and extends longitudinally in the casing, and is rotatable therein. The rotor is formed with radial ridges extending helically and longitudinally of the rotor and have edge faces confronting the annular wall of the casing. The blades have their outer surfaces contacting the inner surface of the annular wall of the casing and are thereby pressed inwardly and cut hair against the comb's teeth. This shaver has a motor casing of usual construction, serving as a handle, and positioned outside of the hair-cutting head.
Still another rotary safety razor exists comprising a shaving head having a rotary cutter unit (with helical blades) mounted to rotate about an axis. The head of this rotary safety razor comprises, in combination, a tubular casing adapted to contain the cutter and split along a longitudinal line so as to present a slot with two edges. One of these edges is formed along a major portion of its length with the cutting edge of a stationary straight blade while the other of these edges is formed with a comb opposite the cutting edge. This rotary safety razor addresses the issue of the drive mechanism by placing it outside the shaving head and transferring the rotational motion of the external motor via a shaft formed at one end with a worm engaging worm teeth on a rotatable cutter unit.
Additional motorized shaving apparatus exist that utilize a screen wherein the cutting elements do not come in direct contact with the skin but rather are located behind the screen.